Machine Elements in Mechanical Design

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Answers to Selectecj Problems
Given here are the answers to problems for which there are unique solutions. Many of the problems for solution in this book are true design problems, and individual design decisions are required to arrive at the solutions. Others are ofthe review question form tor which the answers arc in the text ofthe associated chapter It should also be noted that some ofthe problems require the selection ot design factors and the use of data from charts and graphs. Because of the judgment and interpolation required, some ofthe answers may be slightly different from your solutions.

CHAPTER 1 The Nature of Mechanical Design
15. D - 44.5 mm 16. Z. = 14.0 m 17. T= 14l8N-m 18. M = 2658 mm19. S = 2.43 X 10'mm' 20. / = 3.66 X 10'mm" 21. Z. 2 X 2 X 3/8 22. P = 5.59 kW 23. .v„ = 876 MPa 24. Weight = 48.9 N 25. T= 20.3 N-m H = 0.611 rad Scale = 5.14 1b-in/deg Scale = 33.3 N-m/rad 26 Energy = 1.03 x 10" Ib-ft/yr Energy = 3.88 X lO'W-h/yr 27 M = 540 Ib • s/ftp = 25.9 X lO'N-s/m4.60 X 10' rev

24. AISI 12L13 steel has lead added to improve machinability. 25. AISI 1045, 4140, 4640, 5150. 6150, 8650. 26. AISI 1045. 4140. 4340, 4640, 5150, 6150, 8650. 27. Wear resi.stance, strength, ductility. AISI 1080. 28. AISI 5160 OQT 1000 is a chromium steel, having nominally 0.80 percent chromium and 0.60 percent carbon, a high carbon alloy steel. It has fairly high strength and good ductility. It was through-hardened, quenched in oil, and tempered at 1000°F. 29. Yes. with careful specitlcadon ofthe quenching medium. A hardness of HRC 40 is equivalent to HB 375. Appendix 3 indicates that oil quenching would not produce an adequate hardness. However, Appendix 4-1 shows that a hardness of HB 400 could be obtained by quenching in water and tempering in 700°F while still having 207f elongation for gciod ductility. 33. AISI 200 and 300 series 34. Chromium 35. ASTM A992 structural steel 37. Gray iron, ductile iron, malleable iron 41. Stamping dies, punches, gages 43. Strain hardened 46. Alloy 6061 50. Gears and bearings 60. Auto and truck bodies; large housings

CHAPTER 2

Materials in Mechanical Design

9. No. The percent elongation must be greater than 5.0 percent to be ductile. 11. G = 42.9 GPa 12. Hardness = 52.8 HRC 13. Tensile strength = 235 ksi (Approximately) Questions 14-17 ask what is wrong with the given statements. 14. Annealed steels typically have hardness values in the range from 120 HB to 200 HB. A hardness of 750 HB is extremely hard and characteristic of as-quenched high alloy steels, 15. The HRB scale is normally limited to HRB 100. 16. The HRC hardness is normally no lower than HRC 20. 17. The given relationship between hardness and tensile strength is only valid for steels. 18. Charpy and Izod 19. Iron and carbon. Manganese and other elements are often present. 20. Iron, carbon, manganese, nickel, chromium, molybdenum. 21. Approximately 0.40 percent. 22. Low carbon: Less than 0.30 percent Medium carbon: 0.30 to 0.50 percent High carbon: 0.50 to 0.95 percent 23. Nominally 1.0 percent.

CHAPTER 3

Stress Analysis

1. a = 31.8 MPa; 6 = 0.12 mm 2. CT = 44.6 MPa 3. CT = 66.7 MPa 4. CT = 5375 psi 5. CT = 17 200 psi 6. For all materials,CT= 34.7 MPa Deflection: a. 6 = 0.277 mm c. 8 = 0.377 mm e. 8 = 0.503 mm g. 8 = 7.56 mm. b. 8 = 0.277 mm d. 8 = 0.830 mm f. 8 = 23.8 mm

A-44

Answers to Selected Problems

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43. 93 750 N-mm 45. 8640 lb in 47. - I I 250 N • mm 49. - 1 . 4 9 kN-m 51. CT = 62.07 MPa 53. a.CT= 20.94 MPa tension on top of lever

A-45

Note: The stress is close to the ultimate strength for (f) and (g). 7. Force = 2556 lb;CT= 2506 psi 8. CT = 595 psi 9. Force = 1061 lb 10. D = 0.274 in 13. CTAD = ODE = 6198 psi

CTgp = 7748 psi CT BD = 0 psi
CTBE = 5165 psi O"AB

b. At section B, h = 35.1 mm; at C, /i = 18 mm 55. CT = 84.6 MPa tension 57. Sides = 0.50 in 59. MaximumCT= - 1.42 MPa compression on the top surface between A and C 61....
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